The present invention relates to methods and apparatus for detecting defective knitting needles in a circular knitting machine in which each hooked needle in a revolving circular array is reciprocated in succession during knitting, so that the hooked end is moved a distance into an outstanding or upstanding position relative to the other hooked ends and then returned to substantially the same plane in which the other hooked ends are disposed when not being reciprocated.
Some defects such as a very slightly bent needle do not cause difficulties during knitting, but other defects such as the snapping off of a needle hook or the jamming of a needle latch in its hook-closing position are unacceptable since they cause the production of malformed fabric with a ladder fault knitting therein.
According to one aspect of the invention a method of detecting a defective knitting needle in a circular knitting machine comprises directing a beam of light across the path of travel of the knitting needles onto photoelectric means such that a hook at one end of an intact or proper needle, whose latch is open, enters the beam to cast a shadow on the photoelectric means not latter in time than any other part of the needle entering the beam casts its shadow on said photoelectric means, and detecting from an output of the photoelectric means when the shadow cast by the said end occurs later in time than that of said other part or parts to indicate a defect.
According to a second aspect of the invention there is provided a circular knitting machine comprising a circular array of knitting needles rotatable in a circular path, a first photoelectric means disposed at a higher vertical position than a second photoelectric means, a light source arranged to direct a beam of light onto said photoelectric means, an arc of said circular path passing between the light source and the photoelectric means such that when the needles are rotated along the needle path, each passes in succession through the beam and casts a shadow of the end of the needle having the hook onto the first photoelectric means and also casts a shadow of the thinner part of the shank of the needle or a jammed closed needle latch onto the second photoelectric means. The beam is directed so that when a proper needle with an intact hook and open latch enters the beam, the shadow of the hook is cast on the first photoelectric means before the shadow of any other part of the needle is cast on the second photoelectric means. However, if the hook is broken off a shadow of the shank is cast onto the second photoelectric means before any shadow of the needle is cast onto the first photoelectric means, of if the latch is jammed closed a shadow of the latch is cast onto the second photoelectric means before any shadow of the needle is cast onto the first photoelectric means. The photoelectric means is connected to control means wherein first and second electric signals are provided corresponding to shadows cast onto the first and second photoelectric means respectively when the machine is in use, and the control means is arranged to initiate stopping of the machine and/or operation of warning means, whenever a signal from the second photoelectric means for a given needle appears or occurs before the signal from the first photoelectric means for shadows cast by that same needle.
It has been found that the method of detecting defective knitting needles according to the first aspect of the invention or the use of apparatus according to the second aspect of the invention to detect defective knitting needles may fail to detect a faulty needle in certain unusual cases where a needle is snapped off so low down its shank that the photoelectric means may not have a shadow of this badly broken needle cast thereon. This is because the stump of the shank is too low and does not interrupt the light beam, and therefore no signal is issued to indicate this defect condition.
To remedy this there is provided according to a third aspect of the invention a method of detecting a defective knitting needle in a circular knitting machine comprising directing onto photoelectric means a beam of light which is interrupted by knitting needles travelling in a circular path and successively entering the beam, the photoelectric means comprising first photoelectric means disposed above second photoelectric means, and third photoelectric means offset in a horizontal direction from the first and second photoelectric means, arranging the first photoelectric means for the shadow of an intact hooked end of a first needle to be cast thereon before a shadow of the shank or a closed latch portion of the first needle is cast on the second photoelectric means, but also arraying the first and second photoelectric means for the shadow of the first needle, should it have a broken hook or a latch jammed in the closed or substantially closed position, to be first cast on the second photoelectric means, and arranging the third photoelectric means for a shadow of a second knitting needle to be cast thereon after the hooked end of the first needle has cast a shadow on the first photoelectric means. Variations in electrical outputs from the first, second and third photoelectric means due to needle shadows cast thereon are detected, said outputs are fed to control means responsive in the absence of an electrical cancel signal to the variation in output from the second and third photoelectric means to cause halting of the knitting machine and/or operation of alarm means, and the operation of the control means to prevent halting of the machine and/or operation of the alarm means is inhibited by feeding to the control means the cancel signal generated upon the appearance of the variation in output from the first photoelectric means. The cancel signal is of a predetermined duration of sufficient length for the output variation from the second and third photoelectric means to appear and disappear within the duration of the cancel signal.
According to a fourth aspect of the invention there is provided a knitting machine according to the second aspect comprising third photoelectric means offset along the needle paths from the first and second photoelectric means and arranged for the light source to illuminate the third photoelectric means such that after a first needle having an intact hook and open latch has cast a shadow onto the first and second photoelectric means a second needle passing through the beam casts a shadow onto the third photoelectric means, the third photoelectric means being connected to the control means wherein a third signal is provided corresponding to the shadow cast onto the third photoelectric means. The arrangement is such that the first signal has a duration which is longer than the time between the appearance of the second signal and the disappearance of the third signal, but if no first signal is produced because a needle is broken too low down to interrupt the beam and the next needle then interrupts the beam to cast a shadow on the third photoelectric means the corresponding third signal appears and in the absence of the first signal the control means initiates stopping of the machine and/or operation of warning means.
Each aspect of the invention will now be further described by way of example with reference to the accompanying drawings.